The present invention relates to a method for producing a single crystal and, in particular, to a method enabling production of a single crystal in various complex shapes without subjecting it to any cutting or grinding process.
Various methods for producing single crystals are known in the art, including pull-up methods (such as the Czochralski process) and pull-down methods (such as the Bridgman technique). Under the pull-up method, a material sought to be crystallized is first placed into a crucible made of a material such as quartz or carbon and is heated into a melt. A single-crystal ingot is produced by dipping and rotating a seed crystal in the melt and gradually pulling it upward. The pull-down method utilizes a suitable temperature distribution within a furnace, wherein a melt solidifies to form a single-crystal ingot from the bottom of a furnace vessel containing the melt either by moving the vessel downward or by lowering the temperature of the furnace.
Since the single crystal produced by either of the above-described two methods is in the form of an ingot, it is necessary to cut and grind the ingot into desired shapes. This necessitates the use of a cutting apparatus and a grinding apparatus, and also requires some processing work. In addition, a certain amount of crystal is wasted in each process.
Furthermore, the cut section may be damaged during the cutting process, resulting in deterioration of the crystal quality. In order to counter this problem, it would be necessary to grind off the surfaces that have been damaged by the cutting process. But this additional process would increase the production cost.
The present invention has been made in light of the above-described problems experienced in the art. The present invention provides a method and apparatus enabling production of a single crystal in desired shapes without subjecting it to any cutting process or grinding process which may be necessary to remove surfaces damaged by the cutting process.
According to the present invention, a material sought to be crystallized is supplied into a vessel that has an interior space of a desired shape. The vessel is then heated to turn the material into a melt in such a manner as to create a temperature distribution in the melt so that symmetrical convection flows of the melt will occur within the interior space. The vessel is then gradually cooled off from the bottom of the interior space, while maintaining the symmetrical convection flows, to crystallize the melt into a shape coincident with the shape of the interior space.
The present invention makes it possible to produce a high-quality single crystal having a desired shape without subjecting it to any cutting process or grinding process that may be necessary to remove surfaces damaged by the cutting process.